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71.
72.
The dielectric constant, dielectric loss, and ac conductivity of polyblends of cellulose acetate hydrogen phthalate (CAP) and poly (vinyl pyrrolidone) (PVP) of different compositions were measured in the temperature range of 300–430 K and in the frequency range of 50 Hz–100 kHz. In the blends, the dielectric constant as well as the dielectric loss as a function of the temperature display a single peak corresponding to the glass transition temperature (Tg) in the region between the Tg values of the pure polymers. The Tg values observed agree well with those values obtained from DSC. Dielectric studies show that CAP forms a miscible blend with PVP. Ac conductivity values were calculated from the dielectric data and the conduction mechanism is discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1702–1708, 2002 相似文献
73.
74.
为了更好地辨别低照度图像中的目标,提高图像的对比度并增强纹理细节信息,采用子层分割规定化算法对图像进行增强处理,提出一种结合子层分割和自适应函数引导的规定化图像增强算法.首先根据原始图像直方图的特点对直方图进行子层分割,之后通过对分割后的子层进行灰度区间拉伸来提高图像的亮度,以增强图像的对比度;为了增强图像中的细节信息,在每个子层求取自适应函数来对每个子层做规定化处理;最后对子层直方图合并,得到增强后图像.实验结果证明,经过增强后图像的灰度平均梯度值为原始图像的3~4倍,信息熵也明显增大;该算法在增强图像细节、提高图像的对比度上具有优越性. 相似文献
75.
Blends of sulfonated phenylated polytriphenylene oxide and poly(methyl methacrylate‐co‐4‐vinyl pyridine) were examined by dynamic mechanical, Fourier transform infrared, and NMR techniques. A high degree of miscibility was evident from a single drop in a plot of the storage modulus versus the temperature. The presence of ionic moieties due to proton transfer from sulfonic acid to 4‐vinyl pyridine was confirmed by both NMR and IR spectroscopy studies. The coils were found to be close to one another in dimethyl sulfoxide‐d6 because the aromatic shielding effect of the phenyl rings of the phenylated polytriphenylene oxide units was observed from the upfield shift of most of the protons of poly(methyl methacrylate) in the NMR spectrum. However, the absence of cross peaks in the nuclear Overhauser and exchange spectroscopy experiments suggested that the intermolecular distance between the chains had to be larger than 4 Å. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 728–733, 2003 相似文献
76.
Rinaldo Gregorio Matheus Rigobelo Chaud Wilson Nunes Dos Santos Joo Baptista Baldo 《应用聚合物科学杂志》2002,85(7):1362-1369
This study presents an investigation of the effect of the different crystalline phases of each blend component on miscibility when blending poly(vinylidene fluoride) (PVDF) and its copolymer poly[(vinylidene fluoride)‐ran‐trifluorethylene] [P(VDF–TrFE)] containing 72 mol % of VDF. It was found that, when both components crystallized in their ferroelectric phase, the PVDF showed a strong effect on the crystallinity and phase‐transition temperature of the copolymer, indicating partial miscibility in the crystalline state. On the other hand, immiscibility was observed when both components, after melting, were crystallized in their paraelectric phase. In this case, however, a decrease in crystallization temperatures suggested a strong interaction between monomers in the liquid state. Blend morphologies indicated that, in spite of the lack of miscibility in the crystalline state, there is at least miscibility between PVDF and P(VDF–TrFE) in the liquid state, and that a very intimate mixture of the two phases on the lamellar level can be maintained upon crystallization. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1362–1369, 2002 相似文献
77.
Mixtures of tetrahydrofuran (THF) and carbon dioxide (CO2) were identified as new solvent systems for polysulfone. The miscibility and density of polysulfone in binary fluid mixtures of THF and CO2 were investigated from 300 to 425 K at pressures up to 70 MPa. The influence of the CO2 and polysulfone concentrations was studied, with the concentrations of the other two components kept constant. At a 4.5 wt % polymer concentration, the demixing pressures in a 10 wt % CO2 and 90 wt % THF mixture increased with temperature (310–425 K) from 15 to 40 MPa. With increasing CO2 concentration (from ca. 10 to 14 wt %), a significant increase (from 15 to 70 MPa at 310 K) was observed in the demixing pressures. Furthermore, with an increasing amount of CO2, the nature of the phase boundary shifted from lower critical solution temperature behavior to upper critical solution temperature behavior. The influence of the polymer concentration was studied in the 0–5 wt % range at two CO2 levels, with solvent compositions of 10 wt % CO2 and 90 wt % THF and 13 wt % CO2 and 87 wt % THF. The system with a higher level of CO2 (13 wt %) showed highly unusual phase behavior: on pressure–composition and temperature–composition diagrams, the system displayed two distinct regions of miscibility. In the system with 10 wt % CO2, the distinct regions of miscibility that were observed in the system with 13 wt % CO2 partially overlapped and led to a W‐shape phase boundary. The densities of the polymer solutions were measured from the one‐phase region through the demixing point into the two‐phase region at a constant temperature. No significant change in density was found around the phase boundary; this indicated that the coexisting phases had similar densities, as is often the case with liquid–liquid phase separation in polymer solutions under high pressure. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2357–2362, 2002 相似文献
78.
数字化的图像处理技术里面对于各个综合知识的跨度是相当大的,对于各个知识面的要求也是十分高的。那么图像处理技术在实际的生活应用中也是被广泛运用。随着科技时代的到来,人们对于图像的画质要求更高,所以对于图像处理技术的研发已经是整个行业必须解决的问题。那么在这样一个要求越来越高的情形下,在视频监控行业里面图像处理技术起到了那些作用?是怎么样去应用到安防监控行业里面的?本文针对这些问题作出了一些简单的讨论和研究。 相似文献
79.
This paper deals with the problem of single-channel noise reduction in the short-time Fourier transform (STFT) domain. Many algorithms have been developed to solve this important problem, most of which generally assume that the STFT coefficients in different frequency bands are uncorrelated, so the noise reduction is achieved by applying a gain function to the STFT of the noisy speech in each frequency band. However, this assumption is not accurate and the STFT coefficients of speech signals between neighboring frequency bands are correlated in practice due to the use of small lengths of the fast Fourier transform (FFT) and overlap add/save techniques in implementation. This paper formulates the noise reduction problem by taking into account the interband correlation using the so-called bifrequency spectrum. Based on this formulation, a single-channel minimum variance distortionless response (MVDR) filter is derived, which is shown to be able to significantly improve the signal-to-noise ratio (SNR) and meanwhile maintain the desired speech not much distorted. Simulations are presented to justify the claimed merits of the developed MVDR filter. 相似文献
80.
随着社会的飞速发展,采集保存视频/图像已经成为人类日常生活的一部分。视频图像的质量高低,对人类识别图像对象起着非常重要的作用。为了改善图像的视觉效果,有目的地强调图像的某些特征,增加图像的可读性与可识别性,提出采取融合增强术来提高视频图像的对比度与清晰度,提高图像增强质量。 相似文献